The present document is based on Japanese Priority Document JP 2001-213438, filed in the Japanese Patent Office on Jul.13, 2001, the entire contents of which being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a manufacturing method of a magnetic memory device. More particularly, the present invention relates to a manufacturing method of a magnetic memory device utilizing a TMR (Tunnel Magneto-Resistive) film.
2. Description of the Related Art
Along with rapid growth of information communicating apparatuses, particularly in the field of personal-use down-sized communication apparatuses such as a PDA (Personal Digital Assistant), higher integration, faster speed, and lower power consumption are demanded against memory elements and logic elements available for constituting these communicating apparatuses. In particular, realization of higher density and greater capacity of non-volatile memories has become a more important issue for the art of replacing such a hard disk or an optical disk which is intrinsically unable to be down-sized due to presence of moving elements.
There is a flash memory based on a semiconductor technology and a FRAM Ferro-electric Random Access Memory) base on a ferro-dielectric technology as such non-volatile memories, for example. Nevertheless, a flash memory still has a problem to solve in that a writing speed still remains in the order of micro-seconds. On the other hand, a FRAM also still has a problem to solve in that re-writable rounds are still insufficient.
A magnetic memory called a MRAM (Magnetic Random Access Memory) described in the IEEE Trans. Magn. 33 (1997), Page 4498, by Wang et al., draws attention as a non-volatile memory which is free from the above-referred problems, and due to the result of improvement in physical characteristics of a TMR (Tunnel Magneto-Resistive) material in recent years, the MRAM memory has drawn attention in this field.
Because of its simple constitution, the MRAM memory can readily be formed into highly integrated configuration. Inasmuch as the MRAM memory executes recording by rotation of magnetic moment, it is possible to secure sufficient re-writable rounds. Further, it is expected that the MRAM memory can execute accessing operation at an extremely high speed rate. Actually, it is already confirmed that the MRAM memory operates itself in order of nano-seconds.
As described above, the MRAM memory advantageously facilitates its own high-integration. However, in the case of actually embodying it, a micro forming fabrication of the above-referred TMR elements is extremely important. Variation of resistance is caused by a tunnel phenomenon generated in an extremely thin insulating film representing aluminum oxide sandwiched by ferro-magnetic elements. Normally, such extremely thin insulating film has a maximum of lnm in thickness. In the event that a metal film adheres to the side of an insulating film, a leakage path is formed, and accordingly, the change of the resistance is lowered significantly. Therefore, it is quite essential to secure such a processing technology to prevent a metal film from re-ahering itself to the side of the insulating film. As to the connection of the TMR elements and the signal wiring (bit line), it is preferred to use a self-alignment type forming technology for the connecting holes. There are proposed following conventional methods in forming the above mentioned TMR elements.
A first manufacturing method utilizes a lift-off method. This technology is widely used for forming an abut junction of a thin-film magnetic head available for a hard disk drive. Using photo-resist for mask material in forming elements, this method continuously executes an etching process and a film-forming process, and then removes the formed film material on the photo-resist in conjunction with the resist. This method features an advantage to form connecting holes by a self-alignment technology.
A second manufacturing method is conventionally available by those steps including; a step of processing a TMR element, a step of forming a film of insulating material and a final step of forming connecting holes by an RIE (Reactive Ion Etching) process with the resist as a mask.
A third manufacturing method executes those steps including the following. Initially, this method forms a metal film by a sputtering process, where the metal film becomes a plug on a TMR film, followed by a step of leveling off the metal film by a lithographic process, followed by a step of forming an insulating film, and execution of a chemical-mechanical polishing process. This method enables the forming of connecting holes by the self-alignment processing.
As described above, it is quite difficult to compatibly secure processing precision and the forming of connecting holes by self-alignment processing, and yet, it is urged to achieve both objectives.
Nevertheless, in order to realize selective film forming by the lift-off process corresponding to the first method, as shown in FIG. 7, it is required to separate a formed film 721 at an end portion of a resist pattern 711. To achieve this, it is essential to introduce a special pattern-forming technology for forming an undercut on a bottom side of the resist pattern 711. This means that, along with further fining of film configuration, contact areas of the resist and a substrate become narrower than that predetermined by a design rule, and thus, it is expected that preservation of a film configuration will become extremely difficult.
In the case of executing the second method, as described earlier, it is required to properly set margin upon consideration of the alignment between elements and connecting holes and dimensional variation, thus obstructing contraction of the design rule.
Further when executing the third method, it is essential to process a plug. However, this process causes precision in the processing of a TMR element, in other words, this process causes extreme declination of precision of the processed form and processed depth.
In order to fully solve the above problems, the present invention provides a novel manufacturing method of a magnetic memory device.
The manufacturing method of a magnetic memory device of the present invention, the manufacturing method comprises a step of processing a magneto-resistive effect film comprising a tunnel barrier layer arranged between a magnetic pinned layer and a memory layer into a predetermined form of an element using a mask layer having a predetermined form of an element, wherein the mask layer is formed by a plating method.
Namely, after forming a foundation layer, a TMR (Tunnel Magneto-Resistive) effect film, a top-coating layer, and a plate-foundation layer sequentially on a substrate, a resist film having an aperture portion of the same shape as predetermined form of an element is formed on the plate foundation layer. Next, by applying a plating method, a plated layer is formed by selectively growing the resist layer on the plate foundation layer inside of the aperture portion. Next, after removing the resist layer, a set of processing is applied from the plate foundation layer up to the memory layer of the magneto-resistive effect film using the plated layer as a mask layer to form a TMR (Tunnel Magneto-Resistive) element.
In the manufacturing method of the above-mentioned magnetic memory device, a plated layer is formed by selectively growing within the aperture portion formed at the resist film by plating method, then a TMR element is formed with the plated layer as a mask layer, so that it is possible to form a self-aligned contact by connecting a word writing line to the above-mentioned plated layer, because the connection of the TMR element and the word writing line can be done through the plated layer.
Further, according to the manufacturing method of the present invention, a special form of resist for the lift-off process is not necessary, it is possible to form a still finer TMR element.
Further, after the aperture portion is formed at the resist, the plated layer which becomes a connection portion is formed utilizing the aperture portion by a plating method, so that an application of a hole miniaturizing technology becomes possible, and further a forming of an aperture portion having such a dimension below critical limit of resolution of a photolithography machine becomes possible, thereby it is possible to form a TMR element having such a dimension below critical limit of resolution.
Further, by way of forming a mask layer with a conductor such as metal, for example, by a selective plating method, it is possible to form a mask layer with high resistance against etching effect, and thus, controllability of the configuration and etching depth are respectively improved.
According to the manufacturing method of the magnetic memory, when connecting the TMR element to the word writing line, it is possible to form such a self-aligning connecting hole. Further, the method of the present invention does not require a special form of resist for the lift-off process, it is possible to form a finer TMR element. Further, the method makes it possible to apply such a hole-miniaturizing technique and form a TVR element having a dimension below critical limit of resolution of any photolithography apparatus. Further, based on a selective plating method, a plated layer made from metal is formed and then utilizes the formed plated layer to serve as the mask layer. As a result, it is possible to improve controllability on the form and the etching depth as well. By virtue of the arrangement and practical effect of the present invention, it is possible to form finer elements, and yet, improve degree of integrating MRAMs.